KR101323232B1 - Frequency domain equalization for time varying channels - Google Patents

Abstract

Systems and methods for a wireless communication system are provided. The method includes estimating a time change of a channel, wherein the wireless communication system transmits on the channel. It also includes reducing the estimated time change of the channel from the signal transmitted by the wireless communication system. Iterative processes and components are provided to enable efficient and precise frequency domain equalization. Various process components remove or mitigate the components of channel variation and restore circular convolution so that frequency domain equalization (FDE) structures developed for static channels become valid in time-varying channels. For time-varying channels, a vector is shown that represents the corresponding equivalent degradation between the time domain and the frequency domain depending on the frequency domain equalization. Thus, a time varying erase process is performed and the vector is repeatedly subtracted from the frequency domain equalization. In this way, frequency domain equalization performance is improved in the presence of time varying channels.

Description

Frequency domain equalization for time-varying channels {FREQUENCY DOMAIN EQUALIZATION FOR TIME VARYING CHANNELS}

This application claims priority to US Provisional Patent Application No. 60 / 895,452, entitled "FREQUENCY DOMAIN EQUALIZATION FOR TIME VARYING CHANNELS," filed March 17, 2007, the entire contents of which are incorporated by reference. Incorporated herein. This application also claims priority to US Provisional Patent Application No. 60 / 895,583, entitled "FREQUENCY DOMAIN EQUALIZATION FOR TIME VARYING CHANNELS," filed March 19, 2007, the entire contents of which are incorporated by reference. Hereby incorporated by reference.

The following description generally relates to communication systems and more specifically to mitigating the effects of such channels while applying frequency domain equalization in the presence of time varying channels.

Wireless communication systems are widely used to provide various types of communication content such as, for example, voice, data, and the like. Such systems may be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (eg, bandwidth, transmit power). Examples of such multiple-access systems are code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access systems (FDMA), 3GPP long term evolution (LTE), orthogonal frequency division multiple access (OFDMA) systems It includes.

In general, wireless multiple-access communication systems can simultaneously support communication for multiple wireless terminals communicating with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. Such a communication link may be established through a single-input-single-output system, multiple-input-single-output system, multiple-input-multi-output (MIMO) system.

A MIMO system uses multiple (N _T ) transmit antennas and multiple (N _R ) receive antennas for data transmission. The MIMO channel formed by the N _T transmit antennas and the N _R receive antennas may be broken down into N _S independent channels, also called spatial channels (where N _S ≦ min {N _T , N _R }). In general, each N _S independent channels correspond to a dimension. If additional dimensions created by multiple transmit and receive antennas are used, the MIMO system can provide improved performance (eg, higher throughput and / or better reliability).

MIMO systems also support time division duplex (TDD) and frequency division duplex (FDD) systems. In a time division duplex (TDD) system, the forward and reverse link transmissions are on the same frequency domain such that the principle of reciprocity enables estimation of the forward link channel from the reverse link channel. This allows the access point to extract the transmit beam-forming gain on the forward link when multiple antennas are available at the access point.

Recently, frequency domain equalization (FDE) has been studied to compensate for transmissions of multi-path channels with long impulse response. By converting operations from the time domain to the frequency domain, the FDE can reduce receiver complexity. The development of the FDE is based on the correspondence between the circular convolution of two sequences in the time domain and the element-wise product of their frequency responses. If the information data is forced to be periodic and the channel is assumed to be static (called quasi-static channels) during the transmission of one data block, the spectrum of the received signal is the frequency response of the channel and the transmitted data Is equal to the product of the spectrum. However, the equivalence between the time domain and the frequency domain is no longer true unless the channel is static. Inequality due to time-varying channels degrades the performance of the FDE. As a result, the FDE is not effective to cope with the deformation caused by the time varying channels.

Despite the degradation in performance in time-varying channels, FDEs are applied under the unconditional assumption that the time-varying channel is actually static without correction for channel time changes.

The following description provides a simplified summary to provide a basic understanding of some aspects of the claimed subject matter. This Summary is not an exhaustive overview and is not intended to identify key or critical elements of the claimed subject matter or to delineate the scope. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

Iterative processes and components are provided that enable efficient and precise frequency domain equalization for multiple-input-single-output systems or multiple-input-multiple-output (MIMO) systems. Various processing components eliminate or mitigate components of channel variation so that frequency domain equalization (FDE) structures developed for static channels are valid in time-varying channels. Thus, the bit error rate (BER) performance of frequency domain equalization in time varying channels is improved. Wireless signals are first processed by input components, such as fast Fourier transforms, in which case the first frequency domain equalization is performed. The received radio signals are transformed from the time domain to the frequency domain via a P-point Discrete Fourier Transform, for example, to determine a base value for frequency domain equalization. However, for time-varying channels, a vector β is determined that indicates the corresponding equivalent degradation between the time domain and the frequency domain that depends on the frequency domain equalization. Thus, a time change erasing process is performed, and β is repeatedly subtracted from the frequency domain equalization. In this way, frequency domain equalization performance is improved in the presence of time varying channels.

To the accomplishment of the foregoing and related ends, certain illustrative aspects are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the claimed subject matter can be used and the claimed subject matter is intended to include all such aspects and their equivalents. Other advantages and novel features will become apparent from the following detailed description when considered in conjunction with the drawings.

1 is a high level block diagram of a system provided to illustrate frequency domain equalization in a communication environment.
2 is a high level flow chart of a frequency domain equalization method.
3 and 4 are example processing systems for frequency domain equalization.
5 and 6 show exemplary performance data for frequency domain equalization.
7 and 8 illustrate example logic modules for frequency domain equalization.
9 illustrates an example communications device using frequency domain equalization.
10 and 11 illustrate example communication systems that can be used with frequency domain equalization.

Systems and methods are provided for facilitating frequency domain equalization in a wireless communication system. In one aspect, a method for a wireless communication system is provided. The method includes estimating a time change of a channel, wherein the wireless communication system transmits on the channel. It also includes reducing the estimated time change of the channel from the signal transmitted by the wireless communication system. In one aspect, the time varying components may be repeatedly subtracted from the frequency domain equalization calculations.

Moreover, various aspects are described in connection with a terminal. A terminal may be referred to as a system, user device, subscriber unit, subscriber station, mobile station, mobile device, remote station, remote terminal, access terminal, user terminal, user agent, or user equipment. The user device may be a cellular telephone, a cordless telephone, a session initiation protocol (SIP) telephone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device with wireless connectivity, a module inside the terminal, a host device ( Eg, a card that may be mounted on or embedded within a PCMCIA card, or another processing device that is connected to a wireless modem.

In addition, aspects of the claimed subject matter methods using standard programming and / or engineering techniques to generate software, firmware, hardware, or any combination thereof to control a computer or computing components to practice various aspects of the claimed subject matter. , Devices, or articles of manufacture. The term “article of manufacture” is used herein to include a computer program accessible from any computer readable device, carrier, or media. For example, computer readable media may include magnetic storage devices (eg, hard disks, floppy disks, magnetic strips, etc.), optical disks (eg, CDs, DVDs, etc.), smart cards, and flash memory devices. (Eg, cards, sticks, key drives, etc.), but is not limited to these. It is also to be understood that the carrier may be used to carry computer readable electronic data, such as data used to send and receive voice mail or to access a network such as a cellular network. Of course, those skilled in the art will understand that many modifications can be made to this structure without departing from the scope or spirit of what is described herein.

Referring now to FIG. 1, system 100 illustrates frequency domain equalization for a communications environment. System 100 is provided with components that enable efficient and precise frequency domain equalization for a multiple-input single-output system or multiple-input multiple-output (MIMO) system (or other types of systems described below). Provide an iterative process or a multi-step process. Various processing components remove, mitigate, or reduce the components of channel variation and restore cyclic convolution so that frequency domain equalization (FDE) structures developed for static channels are valid in time-varying channels. Thus, the bit error rate (BER) performance of frequency domain equalization in time varying channels is improved. Wireless signals 110 (including symbols and other structures) are first processed by input processing components 120, such as fast Fourier transforms, in which case the original frequency domain equalization (FDE) is frequency domain equalization. Executed by component 130. The received wireless signals 110 are transformed from the time domain to the frequency domain through a P-point Discrete Fourier Transform, for example, to determine a base value for frequency domain equalization at 130.

However, for time-varying channels, a value β is determined that indicates a corresponding decrease in equivalence between the time domain and the frequency domain depending on the frequency domain equalization component 130. The time varying cancellation component 140 removes or reduces the effect of β by repeatedly subtracting β from the frequency domain equalization at 130. In this way, frequency domain equalization performance is improved in the presence of time varying channels. As shown, the threshold component 150 can be used to determine when the effects of β are removed, reduced or minimized to a target value. For example, it is determined when the signal quality or other performance parameter is above or below the target value set by the threshold. After β is reduced to a target value, an output 160 is generated for each receiver (shown and described below).

In one aspect, system 100 reduces the component of channel change and restores circular convolution so that FDE structures developed for static channels become valid in time-varying channels. According to one aspect, the bit error rate (BER) performance of frequency domain equalization in time varying channels is improved. Time-varying channels produce signal changes that cause a substantial degradation of FDE execution. The received signal in the time domain is given by:

(1)

(One)

here,

ρ represents the number of propagation paths.

h _l (n) is the channel coefficient of the l-th path at time index n in the block.

τ _l is the delay of the l-th path relative to the first path.

{ s _n } is a sequence of transmitted signals. For the use of FDE, {s _n } is forced to be periodic by a cyclic prefix or a unique word extension.

{ r _n } is the received signal.

{ η _n } is the received noise and other interference.

In order to transform the received signals 110 into the frequency domain, a P-point Discrete Fourier Transform (DFT) is applied to the received signals { r _n } as follows:

(2)

(2)

If the channel is static during the period of the DFT processing block, h _l (n) is independent of n . However, the values of h _l (n) change for time-varying channels in Equation 2 above. The term h _l (n) can be broken down into terms of time invariant and time varying amount as follows:

(3)

(3)

Where h _l (0) represents the value of the channel gain of the l-th path at time index 0 in the data block. This term represents the constant (time invariant) component of the channel impulse response in one block.

. f _l (n) is the difference between channel coefficients at time n and time 0 of the l-th path. This term represents the amount of time change from time 0 to time n of the l-th path. The calculation of f _l (n) can be deduced from equation 3 if the values of h _l (n) and h _l (0) can be estimated.

.

From Equations 2 and 3 above, the received signal in the frequency domain can be written as:

(4)

(4)

The first term α on the right side of equation 4 can be simplified as follows:

(5a)

(5a)

Next, the notation is slightly changed by assuming that the channel path delays τ _l are aligned with time sample points, thus replacing τ _l with l in equation 5b.

(5b)

(5b)

Note that path delays are not normally aligned with time samples, but it should be noted that unaligned paths can be broken down into multiple ordered subpaths to obtain a similar final result. Thus, changing the notation does not reduce the generality of the description. Thus, ρ still represents the number of paths, but it is understood that ρ from this point means the total number of sample points covering the delay spread of the channel, including the sub-path decomposition described above. Since { s _n } is periodic, the following equation is true.

(4)

(4)

Thus, α is rewritten as:

(5)

(5)

here,

(6)

(6)

In equation (4), the second term, β is rewritten as follows:

(7)

(7)

Discrete Fourier transform of the product of two sequences {f _l (n)} and { s _{n -l} }

(8)

(8)

With respect to, the simplified expression of equation (4) can be given as:

(11)

(11)

If a channel is assumed to be constant within one DFT processing block period (eg f _l (n) = 0), β is the correspondence between the convolution in the time domain and the corresponding element-wise product in the frequency domain. Is maintained. Thus, the concept of frequency domain equalization can be applied. For time-varying channels, β destroys the corresponding equivalence between the time domain and the frequency domain, and the performance of the frequency domain equalization can be degraded. The value of the amount β depends on the amount of channel change. Thus, as mobility increases, β has a significant value.

It is desirable to remove or substantially reduce the term β due to the time variation of the channel, but this requires prior knowledge of the transmitted signals s _n as well as the channel coefficients. As will be described in more detail later with respect to FIG. 2, an exemplary aspect of multi-step equalization is used to reduce the effects caused by the time variation of the channel. Other methods of estimating and removing β may also be used.

For time-varying channels, the frequency domain equalization is conceptual due to the presence of β in equation (11) because the frequency response of the received signals is no longer the same as the product of the frequency responses and the channel impulse response of the transmitted signals. Not applicable It is desirable to remove or mitigate β so that the FDE can be processed efficiently. From the above formulas (9) and (10), the calculation of β uses:

Values of { f _l (n) }: This can be obtained by the channel estimation method. Thus, using a given channel estimation method algorithm, h _l (n) and h _l (0) can be obtained. The estimation of f _l (n) can be given as:

(9)

(9)

Values of the transmitted sequence { s _nl }: in practice, these values are not known; However, temporary signal estimates obtained by applying FDE to a time varying channel can be used without any processing for time varying components.

As mentioned above, estimating β may be implemented through other techniques. For example, to estimate the time change for a signal, a known pilot tone can be subtracted from the pilot portion of the signals carrying the pilot tones. The pilot tone is known and is therefore a good source for the estimation of β, but because it does not explicitly include the data-carrying portions of the signal, but rather a small portion of the entire signal, it is necessary for the less relevant portions of the signals to the actual decoding of the data. Is an estimate of β.

Another aspect of two steps may be provided. In a first step, frequency domain equalization is performed on time-varying channels to obtain temporary estimates of the transmitted signals. Using these temporary detected symbols and channel estimates, erasure of β is possible. In a second step, after the cancellation of β, frequency domain equalization is performed at least at a later time.

The system 100 may be used with an access terminal or mobile device, for example, to access an SD card, network card, wireless network card, computer (including laptops, desktops, PDAs), cell phones, smartphones, or networks. May be a module such as any suitable terminal that may be used for this purpose. The terminal accesses the network using an access component (not shown). In one example, the connection between the terminal and the access component can be wireless in nature, where the access components can be a base station and the mobile device is a wireless terminal. For example, terminals and base stations may be divided by time division multiple access (TDMA), code division multiple access (CDMA), frequency division multiple access (FDMA), orthogonal frequency division multiplexing (OFDM), FLASH OFDM, orthogonal frequency division multiple access (OFDMA) Communication using any suitable wireless protocol, including but not limited to

The access components can be access nodes associated with a wireless network or a wired network. For this purpose, the access components can be, for example, routers, switches, and the like. The access component can include one or more interfaces, eg, a communication module, for communicating with other network nodes. The access component may also be a base station (or wireless access point) in a cellular type network, where the base stations (or wireless access points) are used to provide wireless coverage areas to multiple subscribers. Such base stations (or wireless access points) may be arranged to provide contiguous areas of coverage to one or more cellular phones and / or other wireless terminals.

2, a frequency domain equalization method 200 is shown. For simplicity of explanation, the methods (and other methods described herein) are shown and described as a series of acts, but some acts are concurrent with other acts than those shown and described herein in accordance with one or more embodiments and It should be understood and appreciated that the method is not limited by the order of the acts, as it may occur in different orders. For example, those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as a state diagram. Moreover, not all illustrated acts may be used to implement a methodology in accordance with the claimed subject matter.

Before proceeding to the specific method 200, some general frequency domain process actions are described:

을 획득하기 위하여 시변 채널들에 대해 FDE를 적용한다. 이는 송신된 신호들의 임시 추정값들을 생성한다. 따라서, 실질적으로 모든 형태의 주파수 영역 등화 구조들이 이 포인트에서 관여될 수 있다. 주파수 영역 등화는 시불변 채널이 아닌 시변 채널에 적용되기 때문에, 오류 심볼 추정들이 발생할 수 있다. Act 1: Temporary Symbol Estimates

Apply FDE to time-varying channels to get. This produces temporary estimates of the transmitted signals. Thus, virtually all types of frequency domain equalization structures can be involved at this point. Since frequency domain equalization is applied to a time varying channel rather than a time invariant channel, error symbol estimates may occur.

Act 2: Compute β from the temporal symbol estimates in Act 1.

(10)

(10)

Act 3: Subtract β from R _k in Equation (4) above . If the estimate of β is acceptable, then R _k will be α. However, in step 2, ideal data detection may not be achieved and a partial amount of interference items is eliminated.

(11)

(11)

Act 4: Apply frequency domain equalization to R _k calculated in Act 3 to obtain symbol estimates . This behavior is similar to Act 2. Since the influence of β is partially reduced, improved symbol estimates can be achieved in this behavior. Thus, the performance of the overall frequency domain equalization is improved.

Referring now to FIG. 2, a detailed process 200 similar to the general actions 1-4 described above is shown. Proceeding to 210 of process 200, an FFT is performed on input radio signals r _n to convert signals from the time domain to the frequency domain. At 212, the repeat flag is reset to zero and this flag will be tested to determine when process 200 is complete (eg, when the threshold condition is met). At 220, frequency domain equalization is performed on the transmitted data from 210. At 224, a symbol detection sequence is performed. This sequence can cause the flag of 212 to change states. A test is run at 230 to determine whether the flag has changed states. If the flag has changed (eg, the flag is still 0), process 200 terminates and the equalized data is output at 234. If the flag has not changed states at 230 (eg flag = 0), the process proceeds to 240 to set the flag to one. In this case, this allows the process 200 to be executed twice.

However, it should be appreciated that process 200 may be executed more than once if desired. For example, a threshold or other parameter may be set for the signal quality at which the execution flag does not change to the desired quality. In addition, the test at 230 may be for a flag number greater than one that causes the process 200 to execute more times. At 250, a unique word is generated, and data prefixes and suffixes can be appended to the process data. This type of data aids the performance of the FFT by making a given signal appear periodic. Cyclic prefixes may also be used at 250. At 260, β calculation is performed as described above. At 270, time change cancellation is performed, where β is subtracted from previous frequency domain equalization calculations. After the erase, the process goes back to 220 for subsequent frequency domain equalization. Note that channel estimation is performed at 280 (eg, during initial processing or in the background) and used by process 200.

Referring now to FIGS. 3 and 4 together, example systems 300 and 400 in accordance with the components and methods described above illustrate frequency domain equalization processing. In connection with FIG. 3, the received wireless signals 310 are processed through a serial to parallel converter 312 and converted through a DFT component 320. Phase and amplitude adjustments are made at 330 and 334 before the IDFT is performed at 340. A parallel to series converter is used at 350 and despreader 360 generates output 370. In connection with FIG. 4, a hybrid approach is shown. Processing block 410 provides similar functionality as described in FIG. A feedback element is added and the output from processing block 410 is summed at 420 with other processed data. Despreader 430 generates intermediate output 440, which output is fed back to summer component 420 through a respreader component that produces β, wherein β is a frequency domain equalization output from block 410. Is ultimately subtracted from 420. The following description provides additional background for the systems 300 and 400 shown in FIGS. 3 and 4.

)의 정수배라고 가정되고; 수정된 채널 B의 6개의 독립적인 경로들에 대한 전력 지연 프로파일은 이하의 표 1에 열거된다. 이상적인 채널 추정을 가정하고 QPSK 변조를 이용하는 코딩되지 않은 시스템의 성능을 고려하자. 16-ary 월시 코드가 확산 코드로서 사용된다. 1024의 FFT 크기를 이용하여, 하나의 송신 블록에서 변조된 심볼들의 수는 64개이다. 채널 B의 최대 초과 지연은 20054/271=74 칩들로 확장하고 80 칩들의 PN 시퀀스는 각각의 데이터 블록으로 삽입된다. 결과적으로, 정보-포함 심볼들의 수는 59개이다. 시뮬레이션 파라미터들은 이하의 표 2에 요약된다.In one aspect, the performance of the methods described above for frequency domain equalization (FDE) in time-varying channels can be evaluated using computer simulation. For example, the DS-CDMA system is an exemplary system that is considered in the simulation. Aspects may also be applied to non-spread spectrum systems. Recommendation Channel B of the vehicle environment described in ITU-R M.1225 is considered. The chip speed is chosen at 3.6864Mbps as in 3x cdm2000; Delay between multi-paths is due to the underlying chip spacing (

Is assumed to be an integer multiple of); The power delay profiles for the six independent paths of the modified channel B are listed in Table 1 below. Assume an ideal channel estimate and consider the performance of an uncoded system using QPSK modulation. The 16-ary Walsh code is used as the spreading code. Using an FFT size of 1024, the number of modulated symbols in one transmission block is 64. The maximum excess delay of channel B extends to 20054/271 = 74 chips and a PN sequence of 80 chips is inserted into each data block. As a result, the number of information-bearing symbols is 59. Simulation parameters are summarized in Table 2 below.

Table 1: Tapped-Delay-Line Parameters for Vehicle Environment

Table 2: Simulation Parameters

Performance improvements have been demonstrated for algorithms using frequency domain linear equalization (FD-LE) and hybrid decision feedback equalization (HDFE). The FD-LE configuration for DS-CDMA is shown in FIG.

The linear equalization coefficients { W _k } are given by:

(12)

(12)

는 백색 잡음 편차(variance)이다.Where { H _k } is the DFT of the channel impulse response,

Is the white noise variance.

One possible realization of DFE in FD is a hybrid structure, where a feed-forward filter is implemented in the frequency domain and a feedback filter is implemented in the time domain. Chip-level HDFE is shown in FIG. 4. It is to be understood that other suitable structures and implementations are possible.

5 and 6 together, exemplary frequency domain performance data is shown. The feedback filter coefficients { β _i } described above can be found by solving a set of linear equations as follows:

(13)

(13)

Where N _b is the number of taps in the feedback filter, and λ _m is defined as

(14)

(14)

The feed-forward filter coefficients are expressed as

(15)

(15)

Aspects of the exemplary method have been evaluated for mobile units traveling at speeds of 60 km / h and 120 km / h and ideal channel estimation is assumed. Simulations are shown at 500 and 510 of FIG. 5. In the medium speed fading channel (v = 60 km / h), a small performance gain is observed. The reason for the proper gain is that at this rate and the selected FFT size, the channel gains do not vary much for one data block. The effect of β in the above equation (4) is almost negligible. However, the assumption that when the mobile unit moves at a speed of 120 km / h violates the assumption that the channel gains remain constant for one block duration. By partially removing the amount of β, the proposed approach includes FDE structures; Better performance than traditional FDE for both FD-LE and chip-level HDFE. Since the performance of the method for FDE in time-varying channels may depend on the accuracy of the data detected in the first stage, chip-level HDFE provides more performance gain than FD-LE in fast fading channels.

Charts 600 and 610 of FIG. 6 illustrate the performance of an algorithm based on practical channel estimation. For the unique word (UW) transmission format, UW may be added to the end of each block and used as pilot signals to estimate the channel. To obtain a more accurate channel estimate, the length of the UW can be extended to 288 chips. Interpolation may be used to obtain channel coefficients in the data field for the time-multiplexed pilot symbol structure. Thus, channel estimation can be performed in two steps: First, the channel at the UW location is estimated using a multi-step serial interference cancellation approach. Second, sync interpolation techniques are used to obtain channel gains in the data field. The interpolation time coefficient may depend on the assumptions made about the channel conditions. For example, if the maximum user speed is 120 km / h and the carrier frequency is 2 GHz, a sync interpolator with 4.5 ms or less between the center and the first null may be appropriate. Any other suitable channel estimation technique may be used.

Referring now to FIGS. 7 and 8 together, systems are provided that relate to a terminal, an operator network, an access node, and a sequence of commands relating to traffic flows therebetween. Systems are represented by a series of interrelated functional blocks, which can represent functions implemented by a processor, software, hardware, firmware, or any suitable combination thereof.

With reference to FIG. 7, shown is a system that facilitates communications from a mobile device. System 700 includes a logic module 702 for determining time variation at a device and a logic module 704 for determining frequency domain equalization at the device. System 700 also includes a logic module 706 for reducing time variation from frequency domain equalization in the device.

Referring now to FIG. 8, shown is a system 800 that facilitates communication from a base station. System 800 includes a logic module 802 for determining time variation at an access point and a logic module 804 for determining frequency domain equalization at an access point. System 800 also includes a logic module 806 for removing time variations from frequency domain equalization at the access point.

9 illustrates a communications device 900 that may be a wireless communications device, such as a wireless terminal. Additionally or alternatively, communication device 900 may reside within a wired network. The communication device 900 can include a memory 902 that can retain instructions for determining a time change for a signal received at a wireless communication terminal, where the time change is subtracted from the frequency domain equalization. Additionally, communications device 900 may include a processor 904 capable of executing instructions in memory 902 and / or instructions received from another network device, wherein the instructions are communications device 900 or It may involve setting up or operating an associated communication device.

Referring now to FIG. 10, shown is a multiple access wireless communication system according to one aspect. The access point 1000 (AP) includes a number of antenna groups, including groups including 1004 and 1006, groups including 1008 and 1010, and additional groups including 1012 and 1014. In FIG. 10, two antennas are shown for each antenna group, although more or fewer antennas may be used for each antenna group. The access terminal 1016 (AT) communicates with the antennas 1012 and 1014, which transmit the information to the access terminal 1016 over the forward link 1020 and transmit the reverse link 1018. Information is received from the access terminal 1016. The access terminal 1022 communicates with the antennas 1006 and 1008, which transmit the information to the access terminal 1022 over the forward link 1026 and the information over the reverse link 1024. Is received from the access terminal 1022. In an FDD system, communication links 1018, 1020, 1024, and 1026 may use different frequencies for communication. For example, the forward link 1020 may use a different frequency than that used by the reverse link 1018.

Each group of antennas and / or the area in which they are designated to communicate is often referred to as a sector of the access point. Each of the antenna groups may be designated to communicate with access terminals in a sector of the areas covered by the access point 1000. In communication over forward links 1020 and 1026, the transmit antennas of access point 1000 are beam-formed to improve the signal-to-noise ratio of the forward link for different access terminals 1016 and 1024. forming). In addition, an access point that uses beamforming to transmit to its randomly distributed access terminals through its coverage may have an access terminal in neighboring cells as compared to an access terminal transmitting over one antenna to all access terminals. With less interference.

An access point may be a fixed station used to communicate with terminals and may be referred to as an access point, a Node B, or some other terminology. An access terminal may be referred to as an access terminal, user equipment (UE), wireless communication device, terminal, access terminal, or some other terminology.

Referring to FIG. 11, a transmitter system 1110 (also known as an access point) and a receiver system 1150 (also known as an access terminal) within the MIMO system 1100 are shown. In the transmitter system 1110, traffic data for multiple data streams is provided from a data source 1112 to a transmit (TX) data processor 1114. Each data stream may be transmitted via a respective transmit antenna. TX data processor 1114 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data.

Coded data for each data stream may be multiplexed with pilot data using Orthogonal Frequency Division Multiplexing (OFDM) techniques. Pilot data is a known data pattern that is generally processed in a known manner and can be used in the receiver system to estimate the channel response. The coded data and the multiplexed pilot for each data stream are then based on a particular modulation scheme selected for the data stream (e.g., BPSK, QPSK, M-PSK, M-QAM, etc.) to provide modulation symbols. It is modulated (eg, symbol mapped). The data rate, coding, and modulation for each data stream can be determined by the instructions performed by the processor 1130.

Modulation symbols for the data streams may then be provided to the TX MIMO processor 1120, which may further process the modulation symbols (eg, for OFDM). TX MIMO processor 1120 then provides an N _T modulation symbol stream to the N _T transmitters (TMTR) 1122a through 1122t. In some embodiments, TX MIMO processor 1120 applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.

Each transmitter 1122 receives and processes each symbol stream to provide one or more analog signals, and further condition (eg, amplify) the analog signal to provide a modulated signal suitable for transmission over a MIMO channel. , Filtering and upconverting). N _T modulated signals from transmitters 1122a through 1122t are then transmitted from N _T antennas 1124a through 1124t, respectively.

In the receiver system 1150, the transmitted and modulated signals are N _R Received by the antennas 1152a through 1152r and received from each antenna 1152 is provided to each receiver (RCVR) 1154a through 1154r. Each receiver 1154 is configured to condition (eg, filter, amplify, and downconvert) each received signal, digitize the conditioned signal to provide samples, and provide a corresponding "received" symbol stream. Process further samples.

The RX data processor 1160 then receives and processes the N _R received symbol streams from the N _R receivers 1154 based on the specific receiver processing technique to provide N _T “detected” symbol streams. RX data processor 1160 then demodulates, deinterleaves, and decodes each detected symbol stream to recover traffic data for the data stream. Processing by the RX data processor 1160 is complementary to that performed by the TX MIMO processor 1120 and the TX data processor 1114 in the transmitter system 1110.

The processor 1170 periodically determines which pre-coding matrix to use (as described below). The processor 1170 may form a reverse link message that includes a matrix index portion and a rank value portion. The reverse link message may include various types of information regarding the communication link and / or the received data stream. The reverse link message can then be processed by the TX data processor 1138, which is also modulated by the modulator 1180 and conditioned by the transmitters 1154a-1154r to provide a transmitter system. Also receives traffic data for multiple data streams from data source 1136, which is sent back to 1110.

In transmitter system 1110, modulated signals from receiver system 1150 are received by antennas 1124, conditioned by receivers 1122, demodulated by demodulator 1140, and an RX data processor. Processed by 1142 to extract the reverse link message sent by receiver system 1150. Processor 1130 then processes the extracted message to determine which precoding matrix will be used to determine beamforming weights.

In one aspect, logical channels are classified into control channels and traffic channels. Logical control channels include a broadcast control channel (BCCH), which is a DL channel for broadcast system control information. The paging control channel (PCCH) is a DL channel for transmitting paging information. The multicast control channel (MCCH) is a point-to-multipoint DL channel used for multimedia broadcast and multicast service (MBMS) scheduling and for transmitting control information for one or more MTCHs. In general, after establishing an RRC connection, this channel is used only by UEs receiving MBMS (Note: Old MCCH + MSCH). Dedicated Control Channel (DCCH) is a point-to-point bidirectional channel used by UEs that transmit dedicated control information and have an RRC connection. Logical traffic channels include a dedicated traffic channel (DTCH), a point-to-point bidirectional channel, dedicated to one UE for transmission of user information. The multicast traffic channel (MTCH) is also a point-to-multipoint DL channel for transmitting traffic data.

Transport Channels are classified into DL and UL. DL transport channels include a broadcast channel (BCH), downlink shared data channel (DL-SDCH) and paging channel (PCH), which map to PHY resources that can be used for other control / traffic channels. And broadcast over the entire cell, for support of UE power savings (DRX cycles are indicated by the network for the UE). UL transport channels include a random access channel (RACH), a request channel (REQCH), an uplink shared data channel (UL-SDCH), and multiple PHY channels. PHY channels include DL channels and a set of UL channels.

DL PHY channels include:

Common Pilot Channel (CPICH)

Synchronization Channel (SCH)

Common Control Channel (CCCH)

Shared DL Control Channel (SDCCH)

Multicast Control Channel (MCCH)

Shared UL Assignment Channel (SUACH)

Acknowledgment Channel (ACKCH)

DL Physical Shared Data Channel (DL-PSDCH)

UL Power Control Channel (UPCCH)

Paging Indicator Channel (PICH)

Load Indicator Channel (LICH)

UL PHY channels include:

Physical Random Access Channel (PRACH)

Channel Quality Indicator Channel (CQICH)

Acknowledgment Channel (ACKCH)

Antenna Subset Indicator Channel (ASICH)

Shared Request Channel (SREQCH)

UL Physical Shared Data Channel (UL-PSDCH)

Broadband Pilot Channel (BPICH)

In one aspect, a channel structure is provided that preserves the low PAR characteristics of a single carrier waveform (at any given time, the channels are continuous and evenly spaced in frequency).

What has been described above includes one or more embodiments. Of course, it is not possible to list every derivable combination of components or methods for the purpose of describing the foregoing embodiments, but one of ordinary skill in the art will recognize that many further combinations and permutations of the various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims. Also, to the extent that the term "include" is used in the description or in the claims, such term includes the term "comprising" as interpreted when "comprising" is used as a transition phrase in a claim. It is intended to be inclusive in a similar manner.

Claims (35)

A method for a wireless communication terminal,
Converting the received signal from the time domain to the frequency domain;
Estimating a time change of a channel, wherein the wireless communication terminal transmits or receives information over the channel, and estimating the time change of the channel comprises: a received signal in the time domain and a frequency domain; Determining a vector that represents a corresponding degradation of the equivalent equivalence between the transformed signals of R 1;
Performing frequency domain equalization for the channel; And
Reducing the estimated time change of the channel from a signal transmitted or received by the wireless communication terminal by subtracting the vector from a frequency domain equalization calculation and by performing the frequency domain equalization on the subtracted result signal.
/ RTI >
Method for a wireless communication terminal. The method of claim 1,
The received signal is:

Represented by the time domain, where
ρ represents the number of propagation paths;
h _l (n) is the channel coefficient of the l-th path at time index n in the block;
τ _l is the delay of the l-th path relative to the first path;
{ s _n } is a sequence of transmitted signals;
{ r _n } is the received signal; And
{ η _n } is the received noise and other interference,
Method for a wireless communication terminal. 3. The method of claim 2,
Generating a fast Fourier transform (FFT) of r _n to produce R _k in the frequency domain,
Method for a wireless communication terminal. The method of claim 3, wherein
The vector is
Time-varying representation:

, Where
f _l (n) is the difference between channel coefficients at time n and time 0 of the l-th path, and

Is a tentative symbol estimate,
Method for a wireless communication terminal. 5. The method of claim 4,
β is subtracted from the frequency domain equalization (FDE) in a recursive manner,
Method for a wireless communication terminal. The method of claim 5, wherein
Subtracting the vector from the frequency domain equalization calculation is

Expressed through,
Method for a wireless communication terminal. The method according to claim 6,
Forcing the sequence to be periodic via a cyclic prefix,
Method for a wireless communication terminal. The method according to claim 6,
Forcing the sequence to be periodic via unique word extension,
Method for a wireless communication terminal. The method of claim 1,
Further comprising using the threshold to determine to reduce the estimated time change,
Method for a wireless communication terminal. The method of claim 9,
The threshold is associated with a signal quality parameter,
Method for a wireless communication terminal. The method of claim 9,
The threshold is associated with the number of iterations,
Method for a wireless communication terminal. The method of claim 1,
Further comprising performing channel estimation to facilitate determination of frequency domain equalization,
Method for a wireless communication terminal. 13. The method of claim 12,
Converting the received signal includes performing at least one discrete Fourier transform to determine the frequency domain equalization,
Method for a wireless communication terminal. The method of claim 13,
Performing a de-spreading function to generate an output from the frequency domain equalization,
Method for a wireless communication terminal. 15. The method of claim 14,
Performing at least a portion of the frequency domain equalization in the time domain,
Method for a wireless communication terminal. The method of claim 15,
Feeding back time domain information to the frequency domain for the frequency domain equalization,
Method for a wireless communication terminal. As a communication device,
Instructions for converting a received signal from a time domain to a frequency domain;
Instructions for determining a time change for the received signal at a wireless communication terminal, wherein determining the time change is characterized by the corresponding equivalence between the received signal in the time domain and the transformed signal in the frequency domain. Determining a vector representing the degradation;
Instructions for performing frequency domain equalization for the channel, wherein the vector is subtracted from the frequency domain equalization calculation to reduce the determined time change; And
Retaining instructions for performing the frequency domain equalization on the subtracted result signal,
Memory; And
The processor executing the instructions
/ RTI >
Communication device. The method of claim 17,
The memory further includes instructions for repeatedly subtracting the vector;
Communication device. The method of claim 18,
The memory further includes instructions for subtracting a portion of the time change in the frequency domain and a portion of the time change in the time domain,
Communication device. The method of claim 19,
The memory further includes instructions for using feedback to determine the time change;
Communication device. As a communication device,
Means for converting the received signal from the time domain to the frequency domain;
Means for determining a time change at a device, wherein the means for determining the time change determines a vector representing a corresponding degradation of the equivalent between a received signal in the time domain and a transformed signal in the frequency domain. Means for performing;
Means for determining frequency domain equalization at the device; And
Means for reducing the time change by subtracting the vector from a frequency domain equalization calculation at the device and performing the frequency domain equalization on the subtracted result signal
Including,
Communication device. 25. A machine-readable medium comprising:
Convert the received signal from the time domain to the frequency domain;
Determining a Time Change at the Device—Determining the Time Change comprises Determining a Vector Representing a Degradation of Corresponding Equivalence Between a Received Signal in the Time Domain and a Converted Signal in the Frequency Domain -;
Determine frequency domain equalization at the device; And
Reducing the time change by subtracting the vector from a frequency domain equalization calculation at the device and performing the frequency domain equalization on the subtracted result signal.
Machine-executable instructions are stored,
Machine-readable medium. 23. The method of claim 22,
Further comprising machine-executable instructions for forcing the sequence to be periodic via cyclic prefix or unique word expansion,
Machine-readable medium. 23. The method of claim 22,
Further comprising machine-executable instructions for performing the portion of the time change cancellation routine in the frequency domain and the portion of the time change cancellation routine in the time domain,
Machine-readable medium. As a processor for executing the following instructions,
The instructions include:
Instructions for converting a received signal from a time domain to a frequency domain;
Instructions for Determining Time Change from Signals Received at the Device—Determining the time change may cause a corresponding degradation of the equivalent signal between the received signal in the time domain and the transformed signal in the frequency domain. Determining a vector to represent;
Instructions for performing frequency domain equalization at the device; And
Instructions for reducing the time change by subtracting the vector from a frequency domain equalization calculation at the device and performing the frequency domain equalization on the subtracted result signal,
Processor. A method for a wireless communication access point,
Converting the received signal from the time domain to the frequency domain;
Estimating a time change of a channel, wherein the wireless communication access point transmits or receives information over the channel, and estimating the time change of the channel comprises: a received signal in the time domain and the frequency domain Determining a vector representing a corresponding degradation of the equivalent signal between the transformed signals at s;
Performing frequency domain equalization for the channel; And
Reducing the estimated time change of the channel from a signal transmitted or received by the wireless communication access point by subtracting the vector from a frequency domain equalization calculation and performing the frequency domain equalization on the subtracted result signal.
/ RTI >
Method for a wireless communication access point. 27. The method of claim 26,
The received signal is:

Is represented in the time domain, where
ρ represents the number of propagation paths;
h _l (n) is the channel coefficient of the l-th path at time index n in the block;
τ _l is the delay of the l-th path relative to the first path;
{ s _n } is a sequence of transmitted signals;
{ r _n } are the received signals; And
{ η _n } is the received noise and other interference,
Method for a wireless communication access point. The method of claim 27,
Generating a fast Fourier transform (FFT) of r _n to produce R _k in the frequency domain,
Method for a wireless communication access point. 29. The method of claim 28,
The vector is
Time-varying representation:

Wherein f _l (n) is the difference between channel coefficients at time n and time 0 of the l-th path,

Is a temporary symbol estimate,
Method for a wireless communication access point. 30. The method of claim 29,
β is subtracted from the frequency domain equalization (FDE) in a recursive manner,
Method for a wireless communication access point. 31. The method of claim 30,
Subtracting the vector from the frequency domain equalization calculation is

Expressed through,
Method for a wireless communication access point. As a communication device,
Instructions for converting a received signal from a time domain to a frequency domain;
Instructions for determining a time change for the received signal at a wireless communication access point, wherein determining the time change is such that a corresponding equivalence between the received signal in the time domain and the converted signal in the frequency domain is determined. Determining a vector that expresses a drop in;
Instructions for performing frequency domain equalization for the channel, wherein the vector is subtracted from the frequency domain equalization calculation to reduce the determined time change; And
Retaining instructions for performing the frequency domain equalization on the subtracted result signal,
Memory; And
The processor executing the instructions
/ RTI >
Communication device. As a communication device,
Means for converting the received signal from the time domain to the frequency domain;
Means for determining a time change at an access point, wherein the means for determining a time change comprises a vector representing a corresponding degradation of the equivalent between a received signal in the time domain and a transformed signal in the frequency domain. Means for determining;
Means for determining frequency domain equalization at the access point; And
Means for reducing the time change by subtracting the vector from a frequency domain equalization calculation at the access point and performing the frequency domain equalization on the subtracted result signal
Including,
Communication device. 25. A machine-readable medium comprising:
Convert the received signal from the time domain to the frequency domain;
Determining a change in time from the signals received at the access point, wherein determining the change in time represents a corresponding degradation of the equivalent between the received signal in the time domain and the transformed signal in the frequency domain. Determining a vector;
Determine frequency domain equalization according to the received signals; And
By subtracting the vector from the frequency domain equalization calculation and by performing the frequency domain equalization on the subtracted result signal to reduce the time variation.
Machine-executable instructions are stored,
Machine-readable medium. As a processor for executing the following instructions,
The instructions include:
Instructions for converting a received signal from a time domain to a frequency domain;
Instructions for Determining Time Change from Signals Received at an Access Point—Determining the time change is such that a corresponding deterioration between the received signal in the time domain and the transformed signal in the frequency domain is degraded. Determining a vector representing an expression;
Instructions for performing frequency domain equalization from the received signals; And
Instructions for reducing the time change by subtracting the vector from a frequency domain equalization calculation at the access point and performing the frequency domain equalization on the subtracted result signal;
Processor.

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